The chemical duplicating paper set called carbonless paper has been known for many years. In this duplicating method, the back side (CB) of the top sheet is coated with microcapsules of a nucleophilic, colorless leuco dye and the front side (CF) of the second sheet is coated with an electrophilic acceptor coating capable of catalyzing oxidation and color development of the leuco dye; when one writes or types on the top sheet, the pressure of the writing or typing ruptures the microcapsules of the CB coating and transfers a colored image of the writing/typing to the second sheet. In commerce, it is often desirable to block out certain areas of the second, third, etc., sheets of business forms, so that the latter sheets may be sent, without certain discount, price or other internal business information, to outside parties. To accomplish this blocking out, desensitizing inks are printed on the CF coating and deactivate the CF coating so that no image from the CB coating is transmitted in these areas. These inks often contain opaque white pigments, like titanium dioxide and calcium carbonate, for easier identification of the ink on the press and on the carbonless paper.
Desensitizing inks which can be printed by letterpress or dry offset printing have been known for many years. The active desensitizing agents or desensitizers in these inks are effective as desensitizers for the carbonless paper, but are hydrophilic and interfere with lithographic or wet offset printing. For example, U.S. Pat. No. 4,039,027, to A. Ishizuka, discloses ethoxylated amines and polyamides, but these hydrophilic desensitizers would react with the acidic fountain solutions used in lithographic printing and either prevent the ink from printing in the desired image areas to be blocked out ("blinding") or cause it to print also in the nonimage area ("scumming"). U.S. Pat. No. 4,078,493, to A. Miyamoto, mentions the impossibility of using lithography for printing desensitizing inks and discloses an unusual dry reverse lithographic printing process, which does not employ fountain solutions for keeping the nonimage areas clean and which can use hydrophilic ethoxylated amines.
For desensitizing inks that can be printed by lithographic or wet offset printing, some unusual hydrophobic desensitizers have been claimed. For example, U.S. Pat. No. 4,101,690, to A. Miyamoto and H. Marsukawa, discloses hydrophobic ethoxylated/propoxylated amines as desensitizers. U.S. Pat. No. 4,287,234, to A. Amon et al, mentions that amines and diamines of high molecular weight cannot be used in lithographic printing and discloses alkoxylated nucleophiles, such as ethoxylated alkylphenols and ethylene oxide/propylene oxide copolymers of low (i.e., hydrophobic) hydrophilic-lipophilic balance (HLB). Although these amine-free adducts are claimed to be effective desensitizers, later patents by A. Amon and R. Weil (see below) plus our experience indicate that compounds containing amine groups are essential for effective desensitizing. U.S. Pat. No. 4,597,793, to Amon and Weil, mentions that ethylene oxide/propylene oxide copolymers are incomplete desensitizers, that adducts containing nucleophilic amino or imino groups have much greater desensitizing effect and discloses low HLB propoxylated polyamines as desensitizers plus emulsified water. Japanese 1,105,776 and 63,139,781 disclose hydrophobic butylene oxide adducts of polyamines as desensitizers for lithographic inks U.S. Pat. No. 4,599,111, to Amon and Weil, discloses as desensitizers alkoxylated compounds bridged by polyisocyanates or polyacids; this bridging is a rather extreme approach to improve the transfer of ithographic desensitizing inks by increasing the molecular weight of the nucleophilic alkoxylated desensitizer.
Since it is the amine groups that are most effective in desensitizing carbonless paper, diluting the concentration of amine groups by adding long poly(propylene oxide) chains (as in U.S. Pat. No. 4,101,690 and 4,597,793) means that much more of hydrophobic polymer is required for effective desensitization, a costly approach. Similarly, using the desensitizer as a viscosity increasing component (as in U.S. Pat. No. 4,599,111) means that more of the expensive desensitizer is used than may be required for effective desensitization, also a costly approach.
Accordingly, the art can benefit from lithographic desensitizing inks made with less costly, simpler, more readily available raw materials.